Insert for a golf club head

ABSTRACT

A golf club having a head portion including a face adapted to strike a ball and an insert mounted on the face. The insert consists essentially of a molded piece prepared by curing a suspension polymerized polymethyl methacrylate powder, including from 2 to 5 percent of a butadiene styrene copolymer containing at least 65 percent butadiene grafted thereto, and a liquid consisting essentially of methyl methacrylate and glycol methacrylate as crosslinking monomers at a temperature at least about 170* F.

United States Patent 1 Dance, Jr.

[ Sept. 17, 1974 INSERT FOR A GOLF CLUB HEAD [76] Inventor: Harry Dance,Jr., 2433 Fifth Ave.,

Knoxville, Tenn. 37917 [22] Filed: Mar. 26, I973 [21] Appl. No.: 345,242

[52] US. Cl. 273/173, 273/D1G. 16

[51] Int. Cl A63b 53/04 [58] Field of Search 273/167-175, 273/DIG. l,DIG. 16; 32/17 [56] References Cited UNITED STATES PATENTS 3,134,5965/1964 Boznos 273/173 3,172,667 3/1965 Baker et a1. 273/173 3,233,9052/1966 Flom 273/173 3,421,766 l/1969 Chmiel et a1. 273/DIG. 16

3,571,900 3/1971 Hardesty 273/173 X OTHER PUBLICATIONS OrthodonticResin, Rocky Mountain Dental Products Co., PO. Box 1887, Denver, Col.80201; 1964;

Modern PlasticsPolycarbonate Resin, 1958; pp. l31-l39 and 218.

April Primary ExaminerRichard J. Apley Attorney, Agent, or FirmFitch,Even, Tabin & Luedeka [57] ABSTRACT A golf club having a head portionincluding a face adapted to strike a ball and an insert mounted on theface. The insert consists essentially of a molded piece prepared bycuring a suspension polymerized polymethyl methacrylate powder,including from 2 to 5 percent of a butadiene styrene copolymercontaining at least 65 percent butadiene grafted thereto, and a liquidconsisting essentially of methyl methacrylate and glycol methacrylate ascrosslinking monomers at a temperature at least about 170 F.

2 Claims, 2 Drawing Figures METHYL METHACRYLATE RESIN PAIENIED SEP 1 7I974 METHACRYLATE RESIN Fig. 2.

INSERT FOR A GOLF CLUB HEAD This invention relates to accessories forgolf clubs and particularly to an insert for the striking face of a woodtype golf club.

Wood-type golf clubs commonly have an insert provided on theball-striking face of the club, frequently for enhancing the clickand/or feel" of the club when it strikes a golf ball. These terms referto the contact of the club with the ball and are well recognized in thegame of golf. Inserts which provide good click and feel appear to helpthe golfer drive the ball longer distances.

Various materials have been suggested heretofore for use as an insert inthe striking face of wood-type golf clubs. These materials have beensuggested heretofore for use as an insert in the striking face ofwood-type golf clubs. These materials have included ivory, metal, andvarious plastic materials. Such materials as ivory are expensive anddifficult to obtain. Hard materials are desirable but metal inserts havebeen found to cut golf balls, hence are not desirable. Partly because oftheir low cost and ready availability, plastic materials have been usedas inserts for golf club faces. However, the plastic inserts usedheretofore have been dead in that they provided a poor click and feel"when the club struck a golf ball.

It is an object of the present invention to provide an insert for theface of a wood-type golf club. It is another object to provide an insertof the type described which provides good click and feel when the clubstrikes a golf ball. Other objects and advantages of the invention willbe recognized from the following description including the drawings inwhich:

FIG. 1 is a representation of a wood-type golf club including an insertand depicting various features of the invention; and

FIG. 2 is a representation, partly cut-away and in section, of an insertfor a wood-type golf club and depicting various features of theinvention.

The present inventor has discovered a novel plastic insert havingspecified properties which provides good click and feel" and whichappears to increase the distance which a golfer can drive a golf ball.Stated generally, the present insert comprises a moldable plasticcomposition including a polymer and an elastomer. More specifically, thematerial employed by the inventor as the insert comprises a suspensionpolymerized polymethyl methacrylate powder, including from 2 to 5percent of a butadiene styrene copolymer containing at least 65 percentbutadiene grafted thereto, and a liquid consisting essentially of methylmethacrylate and glycol methacrylate as cross linking monomers. Thepreferred insert has an impact strength of at least about five poundsper inch (measured by a modified Izod test), water absorption of lessthan about 0.7 milligrams per square centimeter (per American DentalAssociation [ADA] Specification No. 12), a Knoop hardness (surface) ofabout 14 (after wet storage for 7 days at 37C), a flexural strength ofabout 10,000 pounds per square inch (by ADA 12), a tensile strength ofabout 10,6000 pounds per square inch (measured while dry), a tensilestrength of about 10,300 pounds per square inch (measured wet afterstorage in water for 7 days at 37C), and a flexural modulus betweenabout 320,000 and 400,000 pounds per inch. This insert preferably issecured to the face of the golf club employing an adhesive.

As shown in FIG. 1, the present insert 10 is mounted on theball-striking face 12 of a wood-type golf club 14. Normally, the insert10 is embedded in a depression 15 in the face of the club so that theface 16 of the insert becomes a continuation of the face 12 of the club.As desired, grooves 18 frequently are provided across the face of theclub and insert to enhance the degree of control over the flight of theball exerted by the club.

The thickness and size of the disclosed insert is chosen such asprovides assurance that there is sufficient mass of the insert for itsproperties to be effective in propelling the golf ball and that theforce of impact of the club striking a golf ball will not destroy theinsert. In the present insert, a thickness about one fourth inch hasbeen found suitable. Thicker inserts require more plastic hence are moreexpensive, while substantially thinner inserts appear to not provide themore desirable click and feel characteristics. Suitably, such insertshave a volume of about three-fourth cubic inch of plastic composition.

One insert 10 as disclosed herein is depicted in FIG. 2 and comprises aquantity of plastic composition molded into a generally trapezoidalshape having a face 16 and rear portion 20 adapted to be received in amating depression in the face of the golf club 14. The face 16 of theinsert normally is contoured in accordance with specifications set bythe Professional Golfers Association for various kinds of clubs. Asdepicted in FIG. 2, the insert includes a plurality of relatively shortfibers 22 dispersed throughout the insert, preferably in a uniformmanner.

As noted, the present inventor employs a moldable plastic in making hisinsert. To obtain the desired click and feel when the club provided withthe present insert strikes a golf ball, the insert is fabricated of aplastic material having specific properties. One particularly suitableplastic material is a polymer and elastomer based composition. Morespecifically, a proprietary material known as Lucitone 199 sold by L. D.Caulk, P. O. Box 359, Milford, Del., has been found particularlydesirable for use in the manufacture of the present insert. Thismaterial is supplied as a twocomponent system including a particulate orpowdered polymer and elastomer component and a liquid component. Thesecomponents are mixed to provide a moldable composition. Lucitone 199 isan impact resistant dental molding composition comprising a suspensionpolymerized polymethyl methacrylate powder, including from 2 to 5percent of a butadiene styrene copolymer containing at least percentbutadiene grafted thereto, and a liquid consisting essentially of methylmethacrylate and glycol methacrylate as cross linking monomers.

In manufacturing an insert employing Lucitone 199, approximately 28cubic centimeters of polymer and elastomer powder component are admixedwith approximately 8 milligrams of the liquid component to provide amoldable composition. This composition is placed in a two-piece moldhaving a cavity dimensioned to the outside dimensions of the desiredinsert shape and size. The quantity of composition added to the mold isat least sufficient to fill the mold. The mold is closed and sealed asby clamping the two pieces of the mold together using a closing forcesufficient to seal against escape of composition or entry into the moldof foreign materials during subsequent curing of the plasticcomposition. v

The composition, in the closed mold, is heated to cure it. One suitablecuring cycle comprises heating the mold insert for approximately 9 hoursat a temperature of about 170F. The temperature of the insert is thencaused to rise to about 212F over a 1-hour period and held at about 212Ffor approximately 1 additional hour. This relatively long curing periodhas been found preferable to insure that the resultant insert has thosephysical properties which are desirable and which are referred tohereinafter. Alternatively, the molded insert may be cured by heating itfor 2 hours at about 170F, heating it to about 212F over a l-hour periodand holding it at about 212F for an additional hour. During the curingcycle the insert is contained within a closed mold. The mold ismaintained in its closed position by means of applied pressure of amagnitude sufficient to prevent opening of the mold as the plasticcures. In one embodiment, the curing is accomplished by placing thesealed mold in a water bath and heating the water bath as per thedescribed heating cycle.

The cured insert, after removal from the mold, may be attached to theface of the golf club by any of several well-known means for attachingsuch inserts. For example, screws may be passed through the thickness ofthe insert and anchored in the wood golf club head. Preferably, however,the insert is secured to the face of the golf club by means of anadhesive such as an epoxy resin. Other adhesives will be apparent to oneskilled in the art.

An insert prepared in accordance with the procedure outlined above hasbeen found to have an impact strength of at least about 5 foot poundsper inch as measured by a modified Izod test. In this test, specimenswere prepared in accordance with American Dental Association (ADASpecification No. 12). Each of the specifications were broken asdesribed in ADA Specification No. 12. The halves of the specimens werethen mounted in a standard impact tester as described in ASTM D-256 forevaluations of impact strength by the unnotched Izod test. The specimenswere 0.1 inch wide, as mounted, so that the value read from the Izodtester was multiplied by to provide the dimensions: foot pounds perinch. The specimens were mounted so that they stood 17 millimeters abovethe top of the device. This test was conducted dry but the specimenitself was wet, having been stored in water at 37C, as described in ADANo. 12, until the impact test was conducted. This physicalcharacteristic is of importance in that it denotes the ability of thepresent insert to resist breakage when the ball is struck. Plasticmaterials having impact strengths of about 3 foot pounds per inch havebeen noted to break under such impacts. It is believed also that theelastomer contained in the plastic composition contributes to theability of the insert to absorb the energy of impact without breaking.

Sorption of water by an insert, such as when playing on a wet course,can change the performance of the club over its performance when dry.The water sorption of the present insert is less than 0.7 milligrams persquare centimeter (per ADA No. 12) which shows the resistance of theinsert to the sorption of water which could change its performance.

The hardness measured at the surface of the disclosed insert is about 14when measured using a conventional Knoop hardness tester and after thesample had been stored wet at 37C for 7 days. The tensile strength ofthis same material was about 10,300 pounds per square inch (measured perADA 12). The tensile strength of a dry sample is about 10,600 pounds persquare inch (measured per ADA 12). The flexural strength of the insertis about 10,000 pounds per square inch (measured per ADA 12). Thesestrength properties of the insert appear to combine with its impactstrength to prevent breakage during use. The hardness of the insertappears to provide a non-yielding characteristic to the insert when aball is struck such that the ball is better propelled forwardly. Intests, wood type golf clubs fitted with the present inserts were foundto drive a golf ball further than did golf clubs fitted withconventional plastic inserts. Moreover, the present insert produced abetter click and feel when the ball was struck.

The disclosed insert exhibited a flexural modulus of between about320,000 and 400,000 pounds per inch. It is believed that this resiliencyof the insert is in large part established by the elastomer in theinsert and that the degree of resiliency displayed accounts in part forthe observed increase in driving distance obtained when using a golfclub fitted with the present insert.

While a preferred embodimenthas been shown and described, it will beunderstood that there is no intent to limit the invention by suchdisclosure, but rather, it is intended to cover all modifications andalternate constructions falling within the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:

1. In combination, a golf club having a head portion including a faceadapted to strike a ball and an insert mounted on said face, said insertconsisting essentially of a molded piece prepared by curing a suspensionpolymerized polymethyl methacrylate powder, including at least from 2 to5 percent of a butadiene styrene copolymer containing at least 65percent butadiene grafted thereto, and a liquid consisting essentiallyof methyl methacrylate and glycol methacrylates as crosslinking monomersat a temperature at least about F.

2. The insert of claim 1 wherein said insert has a modified Izod impactstrength of at least about 5 foot pounds per inch, water sorption ofless than about 0.7 milligrams per square centimeter, a Knoop surfacehardness of 14, a flexural strength of about 10,000 pounds per squareinch, a tensile strength of about 10,600 pounds per square inch, and aflexural modulus of between about 320,000 and 400,000 pounds per squareinch.

2. The insert of claim 1 wherein said insert has a modified Izod impactstrength of at least about 5 foot pounds per inch, water sorption ofless than about 0.7 milligrams per square centimeter, a Knoop surfacehardness of 14, a flexural strength of about 10, 000 pounds per squareinch, a tensile strength of about 10,600 pounds per square inch, and aflexural modulus of between about 320,000 and 400,000 pounds per squareinch.